I've read that the big fossil fuels (Natural gas/Petroleum, Oil, Coal) and will run out in 40-50 years. The time differs with each fuel, but the consensus is that we'll reach a crisis point around 50 years from now. It is also generally agreed that coal will be last to go, perhaps not completely disappearing for 200 years - at current consumption rates. This is considering the growing population, the increase of industrialization, particularly in China and India (and even in what are called Third World countries). I've also read, particularly about oil, that we will simply not be able to sustain our industry well before we run out of oil. In other words, we will reach a crisis where the countries of the world will need more oil than we're able to produce. There is a "Peak" which is the time in our history when we're producing (farming) as much fuel as we will ever be able to, and this peak will of course be followed by a decreasing amount of fossil fuel production. Some experts say we've already passed or are soon about to pass the peak. Coupled with the fact that the demand for fossil fuel is increasing, time could run out even faster.

So, this is why the phrase "dependence on oil" is so frequently stressed. If we adopted other means of energy (wind, solar, nuclear), we'd save fossil fuel and avoid any kind of crisis, or at worst, fighting over the depleted fuels. That's nothing new: Wars have been (are being) fought over oil. So, 'not having enough to go around' will happen before we completely run out, and that can be just as bad.

Another factor in this equation is that, with shrinking polar caps and the prospect of ice free summers in the Arctic in the near future, areas of the Earth that were previously inaccessible could conceivably be open to oil exploration.

Countries such as Russia, China, Canada and the US are already competing for the rights to do such exploration. If fields the size of Prudhoe Bay in Alaska are discovered, it could extend the length of time fossil fuels are available.

Many scientists suggest that Climate Change as a result of Global Warming will be a more serious problem, and sooner, than a shortage of fossil fuels.